1. Field of the Invention
The present invention relates to a mobile communication system supporting packet data, and more particularly to an apparatus and method for establishing header compression context necessary for header compression/decompression when a channel type for data transfer has been changed.
2. Description of the Related Art
A universal mobile telecommunication service (UMTS) system is the third generation mobile communication system using (3G MCS) wideband code division multiple access (CDMA). 3G MCS system is based on a global system for mobile (GSM) communications. It serves as a European mobile communication system and is being developed into multimedia communication that transfers large-capacity data such as packet data, circuit data, etc. as well as voice service.
FIG. 1 shows the architecture of a conventional mobile communication system. Here, the structure of the UMTS system is shown. Referring to FIG. 1, the UMTS system comprises a core network (CN) 100 and a plurality of radio network subsystems (RNSs) 110 and 120. The plurality of RNSs 110 and 120 configure a UMTS terrestrial radio access network (UTRAN)
The RNSs 110 and 120 comprise radio network controllers (RNCs) 111 and 112 and a plurality of Node Bs 115, 113, 114 and 116. In more detail, the RNS 110 is constituted by the RNC 111 and the Node Bs 113 and 115, and the RNS 120 is constituted by the RNC 112 and the Node Bs 114 and 116. The RNCs 111 and 112 are classified into a serving RNC (SRNC), a drift RNC (DRNC) and a controlling RNC (CRNC) according to their roles. The SRNC manages information of user equipment (UE), and is responsible for data transfer with the CN 100. The DRNC is directly connected to the UE, and the CRNC controls radio resources for each of the Node Bs 113-116.
The RNCs 111 and 112 and the Node Bs 113 to 116 are connected to each other via interfaces called Iub. The RNCs 111 and 112 are connected to each other via an interface called Iur. The UE 130 and the UTRAN are connected to each other via a Uu interface (not shown in FIG. 1). The RNCs 111 and 112 allocate radio resources to the plurality of Node Bs 113 to 116 managed thereby, and the Node Bs 113 to 116 provide the radio resources allocated from the RNCs 111 and 112 to the UE 130. The radio resources are configured cell by cell. The radio resources provided by each Node B are radio resources associated with a specific cell covered by a corresponding Node B. The UE 130 establishes a radio channel using the radio resources associated with the specific cell covered by the Node Bs 113 to 116, such that data is transmitted and received via the established radio channel. Because the UE 130 recognizes only a physical channel configured on a cell-by-cell basis, distinction between the Node B 113-116 and the cell is meaningless. Hereinafter, the terms Node B and cell will be used interchangeably.
With the development of communication technology, packet data service provided by the mobile communication system has developed into broadcast/multicast service that provides identical data from a single data source to a plurality of UEs. The broadcast/multicast service can be divided into cell broadcast service (CBS), i.e., message-centered service, and multimedia broadcast/multicast service (MBMS) supporting a multimedia form such as real-time image and speech, still pictures, text, etc.
The MBMS is a service for sending identical multimedia data such as real-time images, speech, still pictures, text, etc. to a plurality of recipients over a radio network. Because an MBMS data stream must be sent to a plurality of cells in which the UEs are located, the UEs set up a point to point (PTP) connection or a point to multipoint (PTM) connection according to the number of UEs located in a corresponding cell that use the MBMS via the set-up connection, respectively.
The MBMS using the PTP connection is provided via a dedicated channel allocated to each UE. The MBMS using the PTM connection is provided via a common channel that all the UEs located within a corresponding cell can access. An MBMS system counts the number of UEs coupled to the MBMS cell by cell, and determines a channel type to be used for the MBMS according to a count value. When the number of UEs using a specific MBMS within an arbitrary cell varies, the UEs will newly establish a channel based on a new channel type under control of the RNC, respectively. Each UE receives configuration information necessary for using the new channel from the system in order to carry out a new channel setup operation. In case of the MBMS based on the Internet protocol (IP), the configuration information includes many parameters associated with protocol in a wireless zone and the IP.
As described above, because the MBMS provides identical data from a single data source to a plurality of UEs, the identical parameters are used in the IP irrespective of a channel type in the wireless zone. In particular, although the channel type for the MBMS in an arbitrary cell is changed from a PTM channel to a PTP channel, the UEs located in the cell still have the IP-related parameters for the MBMS. Nevertheless, the UE must re-receive a large amount of configuration information to carry out a radio channel setup operation based on a new channel type in the conventional MBMS system. For this reason, there are problems in that radio resources are unnecessarily wasted, which may cause a service delay or cutoff phenomenon.